The incidence of ADHD varies depending on the criteria used for
diagnosis. In the UK the estimate is around 5% of school-aged children (ADDISS,
2004). Similarly, American figures are 3-5% of the childhood population.
This means there will be one or two children with ADHD in every class
(Barkley, 1992). ADD is even less common; it is estimated around 1% of
the child population and it is most common in girls. Researches have
identified AD/HD in all social classes and in every nation and culture
they have studied. However, its prevalence varies across countries,
depending on the diagnostic criteria, methods of assessments and
national practises (Myttas, 2004).
According to medical guidelines the condition is much more common in
males than in females. The ratio of boys to girls diagnosed with ADHD is
at least 4:1. However, this may have to do with referral bias. More boys
than girls tend to be referred to the clinics because boys are typically
more aggressive and create more havoc in the classroom than girls. This
suggests that girls, who are generally less disruptive, may not be
properly diagnosed and, in turn, not given the correct treatment
(Barkley, 1992; Myttas, 2004; ADDISS, 2004).